Combustion chamber hot face refractory lining

ABSTRACT

A refractory lining in a combustion chamber operating in a reducing atmosphere. The lining includes at least one or more Zirconia (Zr)-based refractory lining members comprising one or more Zr-based parts. The Zr-based parts comprise at least 90 wt. %, preferably at least 95 wt. %, of monoclinic ZrO2 and/or partially stabilized ZrO2 and/or fully stabilized ZrO2, wherein the total content of tetragonal and cubic ZrO2 amounts to at least 20 wt. %, preferably more than 35 wt. %, as well as Zr based refractory lining members and methods for manufacturing the Zr based refractory lining members.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 16/332,091,filed Mar. 11, 2019, which is a national stage of PCT/EP2017/075641,filed Oct. 9, 2017, which claims foreign priority to Denmark ApplicationNo. PA 2016 00605, filed Oct. 7, 2016, the disclosures of which areincorporated by reference in their entireties herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present innovation is related to a zirconia based lining materialfor gasification plants, especially for gasification plants in whichsynthesis gas (syngas) is produced in a reducing atmosphere inparticular refractory material for use in the combustion chamber of avessel for producing hydrogen and carbon monoxide rich syngas at hightemperatures above 1000° C. and at high pressures above 20 bar.

2. Description of the Related Art

Syngas is a gas mixture consisting primarily of hydrogen and carbonmonoxide. It can be produced from a variety of hydrocarbon fuel sources,e. g. natural gas, refinery off-gas, LPG or naphtha, by reaction withsteam, air, pure oxygen and/or carbon dioxide at very high temperatures.The syngas is the main feedstock for the production of higher valuefuels and chemicals such as methanol, ammonia and synthetic fuels.

Essentially, there are two different pathways to produce syngas on anindustrial scale using high-temperature reactors. In the non-catalyticprocess, a substoichiometric fuel-air mixture or fuel-oxygen mixture ispartially combusted in a cylindrical reactor at temperatures between1000° C. and 1700° C. and at high pressures of up to 150 bar. The rawsyngas leaves the combustion chamber for downstream treatments with atemperature of more than 1000° C.

In the catalytic pathway, the combustion chamber and a catalyst bed,which equilibrates the syngas, are located in the same cylindricalvessel. Usually, at least one layer, being permeable to gases andcomprising regular shaped or lumpy materials, separates the combustionchamber from the underneath situated catalyst bed. This is necessary inorder to avoid a thermal overstressing of the upper catalyst layer andto prevent any disruptions and agitating of the catalyst bed duringoperation. The uppermost surface of this partition therefore acts as thebottom lining of the combustion chamber, in which temperatures of up to1700° C. (mixed gases) and high process pressures of up to 150 bar areprevailing. The outlet temperature of the syngas from the catalyst bedis between about 850° C. and 1100° C.

The above mentioned reactor pressure vessels are lined on the insidewith a multilayer refractory lining which ensures that the temperatureof the outer steel shell remains appreciably lower than the temperatureof the process gases passing inside the vessels. High aluminarefractories with an Al₂O₃ content 93 wt. % are traditionally used forthe inner wall layer (“hot face”). These coarse ceramic refractories,which typically have low silica and iron content, are dense castables ordense bricks being installed individually or in combination with eachother. For vessels with catalytic operation, the partition between thecombustion zone and the catalytic zone are traditionally also made froma high alumina material. When designing the lining of the combustionchamber, a thermal cycling of the inner hot face material, which inparticular occurs during shut-down and restart of the vessel, shouldalso be taken into account.

Due to the strongly reducing atmosphere, elevated temperatures and highprocess pressures prevailing in the combustion chamber, it has beenfound by the applicant that even extremely high fired and chemicallyultrapure alumina bricks (>99% Al₂O₃, also known as alpha corundumbricks) exhibit a volatilization of solid Al₂O₃. Moreover, we have foundthat this volatilization takes place over time of operation, even thoughthe alumina material has aged in-situ sufficiently. This corrosiveeffect of volatilization, which may vary within the chamber, can bemeasured directly as loss of material or loss of thickness. For example,overall material losses on the combustion chamber's hot face lining ofgreater than 10 gram/day/m² have been determined by the applicant. Themechanism of Al₂O₃-volatilization is formation of gaseous aluminumsub-oxides and/or aluminum hydroxide. In this connection, particularattention must be given to the temperature-dependence of thealumina-volatilization, which is characterized by an exponential growthwith increasing temperature above 1200° C. Therefore, in some cases evenvery small temperature changes of e.g. ±5° C. may have a strong impacton the degree of volatilization of alumina material when applied at hightemperatures.

As part of the syngas flow, these gaseous aluminous products migratefrom the inner lining of the combustion chamber to downstream processstages. Here, during cooling down, they condense out which can lead tofouling of downstream equipment or to pressure drop build-up and tovarious considerable problems which in turn can cause unnecessarytreatment operations and substantial costs. Besides reducing the overallefficiency of individual sections of installation and equipment, even aplugging of process gas channels or tubes has been observed. E.g., whenoperating the catalytic-process, the gaseous alumina solidifies withinthe catalyst bed, thereby creating a layer of crystalline deposit ontothe catalyst shapes. This has the effect of gradually agglomerating thecatalyst shapes together, blocking the flow passages and leading to abuild-up in pressure drop over the catalyst bed as well as a gasmal-distribution, which often results in a premature shut-down forreplacing the top catalyst layer.

Due to the corrosive wear caused by the alumina-volatilization, the riskof a bypass of the hot process gas through the refractory, which e.g.may increase the risk of a potential overheating at the steel shell,which ultimately may require large and very costly repairs, isespecially high in the combustion chamber where the temperature ishighest.

To deal with the aforementioned problem of Al₂O₃-volatilization takingplace in the combustion chamber, several proposals have been submittedwhich, however, only indicate approaches for the design of separatedownstream processes for mitigating the negative impacts taking placehere (e. g. EP 0625 481 B1, US 2014/0332727, WO 2012/131318, EP 0583 211A2). A solution to reduce a priori Al₂O₃-volatilization in thecombustion chamber has not been provided yet.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to overcome the abovementioned disadvantages. This object is achieved by the featurescontained in the independent claims. Advantageous variants of theinvention are described in the accompanying claims.

It is therefore an aspect of the present invention to provide arefractory lining in a combustion chamber operating at temperaturesabove 1000° C. and pressures at least partially above 20 bar preferablyin a reducing atmosphere, such as a combustion chamber for producinghydrogen and carbon monoxide rich gases, with an inner lining layerpresenting an improved resistance against material volatilizationcompared to the above described refractories made from high alumina,even under thermal cycling.

In another object of the present invention, a zirconia (Zr) refractorymaterial for the inner layer of the lining is provided whereby the layerthickness can be adjusted in the range between 100 μm and 250 mm,preferably between 150 μm and 160 mm, in order to meet individualapplication requirements as well as to take into account economicaspects.

These and other advantages are provided by a Zr based refractory liningmember comprising one or more Zr-based parts, wherein the Zr-based partscomprise at least 90 wt. %, preferably at least 95 wt. %, of monoclinicZrO₂ and/or partially stabilized ZrO₂ and/or fully stabilized ZrO₂,wherein the total content of tetragonal and cubic ZrO₂ amounts to atleast 20 wt. %, preferably more than 35 wt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional electro microscopic image showing thestructure of a zirconia based refractory lining member in form of acoating on an Al₂O₃ based refractory material according to theinvention.

FIGS. 2a and 2b show a combustion chamber in a gasification reactor.

FIGS. 3a and 3b show embodiments of Zr based refractory membersaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Compared to Al₂O₃, ZrO₂ reveals a well-known higher thermodynamicstability against reduction at temperatures above 1200° C., which can beequated with a lower affinity to volatilization (Barin, I.:Thermochemical Data of Pure Substances. Wiley-VCH, 2004. ISBN3-527-30993-4). Despite their higher specific weight, zirconiarefractories exhibit a significantly lower thermal conductivity incomparison to the above mentioned dense alumina refractories. Moreover,zirconia refractories exhibit the highest ratio of bulk density tothermal conductivity of all oxidic refractories. This results inadditional significant benefits for special areas of the application,which is described later.

An overview of zirconia and alumina refractories is found for instancein “Handbook of Refractory Materials”, editors G. Routschka and H.Wuthnow; (ISBN 978-3-8027-3162-4).

ZrO₂ appears in form of monoclinic (m), tetragonal (t) and cubic (c)crystal modifications. The transformation from monoclinic to tetragonaland back takes place at approx. 1150° C. on heating and at approx. 800°C. on cooling. This phase transformation is notoriously of significanttechnical importance because this effects a critical volume change.Therefore, this temperature-dependent transformation would induce largestresses and consequently a critical crack formation at temperaturechanges, e. g. during the heat treatment as part of the manufacturing aswell as during later use.

Such critical crack formation can be counteracted by a defined insertionof so-called stabilizers in the ZrO₂ crystal lattice, especially calciumoxide (CaO), magnesium oxide (MgO) and/or yttrium oxide (Y₂O₃), andcerium oxide (CeO₂). Scandium oxide (ScO₃) or ytterbium oxide (YbO₃) isalso used in some cases. Depending on the type and the amount used ofthese stabilizers, a very rough subdivision is made between partiallyand fully stabilized ZrO₂, which, however, says little about thespecific mineralogical composition of the zirconia refractory material.The granular zirconia raw materials used for refractory applications donot have a homogenous microstructure. Even within a grain of fullystabilized zirconia, precipitates of tetragonal and monoclinic zirconiamay be found which also has to be taken into consideration whenformulating and manufacturing a material for a specific application anduse. Furthermore, a more or less pronounced change in mineralogicalcomposition of the zirconia raw material used may occur during thermaltreatment, depending mainly on formulation and parameters of thermaltreatment itself. This has also to be considered when formulating andmanufacturing a material.

In contrast to the t-phase, the so-called t′-phase is formed by adiffusionless transformation from the cubic phase by rapid quenching andis believed to be non-transformable. The t′-phase's quite differentmorphology is characterized by an extremely fine size of the domains.

It is well known that even a small amount of impurities, for examplesuch as silica or alumina, can lead to a clearly measurable decrease ofthe sum content of tetragonal (t) and cubic (c) phase in the zirconiaraw material used due to firing at elevated temperatures (e. g. P. V.Ananthapadmanabhan et al., Journal of Material Science, Vol. 24, 1989,pp. 4432-4436).

Therefore, it may be necessary that the sum content of tetragonal andcubic phase of the zirconia raw material basis must be calculated highenough to ensure that the total content of tetragonal and cubic ZrO₂ inthe final product amounts to at least 20 wt. %, preferably more than 35wt. %.

The measured total content of tetragonal and cubic ZrO₂, using RietfeldX-ray powder diffraction analysis, provides a well-defineddistinguishing characteristic of zirconia refractories. The totalcontent of tetragonal and cubic zirconia is equated to the degree ofstabilization.

In view of the above, thermal treatment of especially large-volumezirconia-based refractory lining members with Zr-based parts with up to250 mm thickness, which would not lead to damages either duringmanufacturing or/and during later use, is assessed as a challenge.Similar considerations apply to embodiments having a very low thickness,e.g. of less than 10 mm.

It has been found by the applicant that the Zr based refractory liningmember according to the invention enables manufacturing and use ofZr-based parts in very thin as well as thick embodiments (e.g. coatedand solid bricks/shaped refractories) showing a high resistance totemperature changes, especially when passing through the criticaltemperature range of approx. 800° C. to 1150° C. The degree of the ZrO₂stabilization (minimum 20 wt. %) efficiently prevents the spreading ofpossible locally appearing damages, which in particular are caused bythermally induced mechanical stresses, even within large-volumeembodiments.

Very thin or thin Zr-based parts may be in form of a coating on a shapedrefractory such as a high alumina brick or on a casted dense aluminarefractory. In other embodiments the Zr-based parts may be thick inwhich case the Zr based refractory lining member may consist of theZr-based part only such as when the Zr based part itself is a shaped Zrbased refractory lining member

It is well known that SiO₂ may preferably be used as a sinteringadditive for production of dense zirconia materials. For the presentpurpose, however, it has been found by the applicant that silica asconstituent of the bonding phase reveals extremely higher chemicalcorrosion susceptibility in reducing atmospheres at temperatures above1000° C., e. g. compared to alumina. Therefore, in order to avoid anundesired formation of volatile siliceous compounds which may lead tofouling of downstream equipment (i.e. waste heat boilers) or toloosening of the member's microstructure and ultimately to destruction,the silica content of the Zr-based parts may be lower than 2.0 wt. %,especially lower than 1.5 wt. % preferably lower than 0.5 wt. %.

According to some advantageous embodiments of the invention, Zr-basedparts of the refractory lining member may contain maximum 6 wt. % ofAl₂O₃, preferably maximum 3.5 wt. of Al₂O₃ such as 2.5 wt. % of Al₂O₃.Al₂O₃ may be present in order to increase in an advantageous manner thecontent of tetragonal ZrO₂. If a crack is developed due to high stressload, a high stress concentration at the crack tip can cause atransformation from the metastable tetragonal ZrO₂ to the monoclinic onebeing associated with a volume expansion, which in turn may push backthe propagation of the crack.

In an unexpected way, this material has proven successful in practicalapplication test under strongly reducing atmosphere, elevatedtemperatures and high process pressures. A noticeableAl₂O₃-volatilization has not been determined. However, if the Al₂O₃content is high, such as above 10 wt. the refractory member may lose atleast strength which in turn may lead to premature wear.

According to other embodiments of the invention, the thickness of theZr-based parts of the zirconia-based refractory lining member is in therange between 100 μm to 250 mm, preferably between 150 μm and 160 mm.

Relatively thin Zr-based parts such as 100 μm-1000 μm are notself-supporting, but may still e.g. be used in special setups where thereduction of Al₂O₃-volatilization is the primary objective. Therefore,an aspect of the present invention is to provide the zirconia-basedrefractory lining member with the Zr-based parts as a coating beingbonded by thermal treatment at temperatures above 1200° C. with aAl₂O₃-based refractory material.

The process for manufacturing such a coated Zr based refractory liningmember comprises the following steps:

-   -   providing a shaped refractory Al₂O₃-based material, optionally        with a corresponding cleaning of the surface to be coated, e. g.        removal of dust,    -   applying a powder dispersion in form of a conditioned carrier        fluid onto at least one surface of the material wherein    -   drying followed by a thermal treatment at a temperature above        1200° C.

An Al₂O₃-based refractory material being an alumina based refractorymaterial comprising at least 40 wt % preferably at least 85 wt % Al₂O₃.

The powder dispersion preferably has a consistency similar tohouse-paints (viscosity of approx. 2000-6000 mPa.$) and may be appliedby way of conventional techniques within the group: spraying, painting,dipping and casting. The coating can be applied several times with theresult that an application of a new layer can be performed on both adried coating as well as onto an already thermal treated one.

Powder dispersions for coating are known from the prior art, where saiddispersions include one or more refractory powdered substances in aconditioned carrier liquid, cf. e.g. EP 1506145 B1.

For the production of a coated Zr-based refractory lining member i.e aZr based refractory lining member, where the Zr-based parts are acoating according to the invention, the dispersion comprises a powder ora powder mixture based on ZrO₂, optionally admixed powdered Al₂O₃,whereby the mineralogical composition of the ZrO₂-carrying ingredientsare calculated in such a manner that, the mineralogical composition ofthe coating according to the invention is obtained after a thermaltreatment at a temperature above 1200° C. at close to atmosphericpressures during manufacturing. Powdered ZrO₂ already more or lessstabilized is preferably used. In this connection, the stabilizingmaterials are in particular the common oxides such as CaO, MgO, CeO₂,Y₂O₃ or mixtures thereof.

The dispersed powder or powder mixture presents an average grain size inthe range of approximately 2.5 μm to 50 μm, in particular in the rangeof 5 μm to 25 μm. The grain size has an influence on the formation ofthe coating layer, i.e. larger gain size means a thicker coating layerand smaller grain size results in higher strength. In an appropriatemanner, the average grain size is larger than 7.5 μm to achieve atargeted thick coating formation.

The grain size may be recognizable in the formed coating whereby theaverage grain size of the obtained coating is in a similar range as inthe original powder mixture with approximately 2.5 μm to 50 μm, inparticular in the range of 5 μm to 25 μm.

The powder or powder mixture is formulated and present in such an amountthat after the thermal treatment the mineralogical composition ischaracterized by that the Zr based parts comprises at least 90 wt. %,preferably at least 95 wt. % of monoclinic ZrO₂ and/or partiallystabilized ZrO₂ and/or completely stabilized ZrO₂, whereby the totalcontent of tetragonal and cubic ZrO₂ is at least 20 wt. %, preferablymore than 35 wt. %, the SiO₂-content is below 2.0 wt. %, especiallylower than 1.5 wt. % preferably below 0.5 wt. %.

Surprisingly, it has been found by the applicant, that the coating ofthe coated Zr based refractory lining member (thin-layered refractorymember) according to the invention is bonded to the alumina refractorysubstrate, even after being exposed to thermal cycling repeatedly.Moreover, its mineralogical composition ensures that it is possible toproduce macroscopically crack-free coating layers which over a largearea can be produced with a coating-thickness of at least 100 μm,preferably more than 150 μm, especially on surfaces made of aluminarefractories as described previously. Desired thicknesses of the coatingmay be 100 μm-800 μm, such as 150 μm-500 μm.

I.e. the mineralogical composition of the Zr based coating on thealumina refractory substrate enables a Zr based refractory lining memberwhich may be ideal for use in e.g. combustion chambers operating attemperatures above 1000° C. and pressures at least partially above 20bar preferably in a reducing atmosphere, such as a combustion chamberfor producing hydrogen and carbon monoxide rich gases. The Zr coatedrefractory linking members may provide an inner lining layer presentingan improved resistance against material volatilization compared to theknown refractories made from high alumina, even under thermal cycling.

In some particularly favorable embodiments of this invention, theaforementioned coated Zr based refractory lining member (thin-layeredzirconia-refractory member) according to the invention is being formedduring application “in situ”. The combination of high temperature and,in particular, high pressure and a reducing atmosphere present in situprovide a stronger compaction which provides an improved adhesion and adecrease in porosity, which in turn results in an additionally improvedprotective function against Al₂O₃-volatilization of thealumina-substrate. The “in situ” formation of the thin-layered membermay be particularly advantageous in existing vessels, as it provides asimple and economic installation of a protective lining in form of acoating on the already existing alumina refractory lining of thecombustion chamber. The existing alumina refractory lining can be inform of shaped refractory or in form of a monolithic refractory such asa dense castable.

During in situ formation, the aforementioned thin-layeredzirconia-refractory member i.e. a Zr-based refractory lining member withZr-based part in form of a coating, is being cured by a combination ofhigh temperature and pressure and reducing atmosphere.

In a special embodiment, the formation of the coating takes place in amulti-step in situ process.

In the multi-step in situ process the dispersed powder or powder mixtureto form the coating is applied “in situ”, where after the Zr-basedrefractory lining member in a first heating step is heated up to atemperature in the range of 100−500° C. or at least 200-300° C. at anelevated pressure of 1-20 bar or at least 5-10 bar, forming an adheredcoating which is at least resistant to e.g. water before introduction ofreactive process gas which may contain steam or in which steam isformed. Temperature in the range of 100−500° C. or at least 200-300° C.at an elevated pressure of 1-20 bar or at least 5-10 bar is above thedew point of water in an inert atmosphere (e.g. nitrogen) which meansthat no or very low amounts of water/substantially no water is presentor formed during the first heating step.

The resistance to water is advantageous as the reactive process gasadded after the first heating step may be a syngas containing hydrogenand carbon monoxide or a hydrocarbon containing gas but also ahydrocarbon containing gas containing steam in which case the adherenceof the coating is particularly important to avoid that the coating is atleast partly washed off.

In a second heating step the coated Zr-based refractory lining member isheated, preferably gradually, to above a minimum of 1000° C., andpreferable in the range 1100-1300° C. in a reducing reactive process gascomprising hydrogen and carbon monoxide and at elevated pressures of atleast 10 bar and preferable at 20 bar or above thereby obtaining abonded coating (firmly connected coating).

Heating of the coating of the Zr-based refractory lining member applied“in-situ” to the temperature range of 1100−1300° C. in a reducingatmosphere at elevated pressure will form a surface layer of zirconiabeing bonded with the Al₂O₃-based refractory material of the existinglining. Due to the elevated pressure in the second heating step thebonded and sintered coating obtained comprises at least 90 wt. %,preferably at least 95 wt. % of monoclinic ZrO₂ and/or partiallystabilized ZrO₂ and/or completely stabilized ZrO₂, whereby the totalcontent of tetragonal and cubic ZrO₂ is at least 20 wt. %, preferablymore than 35 wt. even in case of temperatures below 1200° C.

The gradually increase of temperature may take place through a heatingcurve that is continuous increasing or stepped or it could be acombination of continuous increasing and step wise increasing. The firstand second heating step may be carried out as two well defined steps ormay be carried out in direct continuation of each other.

The types of raw material being used for the production of large-volumezirconia-based refractory members with up to 250 mm thickness such asbricks may be the same as for the coated ones. The only difference maymerely be the significantly coarser grain size distribution, wherebyzirconia is used in the grain size of up to 4 mm.

The batch composition of raw materials used is calculated in such amanner that the mineralogical composition of the shaped refractorymember according to the invention is obtained after the thermaltreatment. For example, the sum content of tetragonal and cubic phase ofthe zirconia raw material basis must be calculated high enough to ensurethat the total content of tetragonal and cubic ZrO₂ in the final productamounts to at least 20 wt. %, preferably more than 35 wt. % as even asmall amount of impurities, for example such as silica or alumina, canlead to a clearly measurable decrease of the sum content of tetragonal(t) and cubic (c) phase in the zirconia raw material used due to firingat elevated temperatures.

In difference to the coated Zr based refractory lining members, acompaction of the crumbly mixture almost exclusively takes place duringshaping, in which the shape of the refractory member is defined, insteadof during thermal treatment. For shaping, various well-known processesmay be used depending, in particular, on number of pieces to be made andcomplexity of desired geometric shape (“Handbook of RefractoryMaterials”, op. cit.). Preferred shaping processes for thick refractorymembers such as 20 mm-250 mm are the use of hydraulic presses or manualramming or casting. The particle size of the batch mixture is 0-4 mm,preferably 0-2.5 mm. The grain size distribution of the batch mixture isnot subject to any restrictions in principle, assuming that shaping ofthe batch is possible. Due to coarser grain size, shaped zirconiarefractory members are fired at temperatures above 1400° C., preferablyabove 1600° C., such as 1400-1800° C. in order to achieve a sufficientstrength. According to one embodiment, the cold crushing strength of thefired members, determined in accordance with EN 993-5, is above 30 MPa,preferably between 50 MPa and 200 MPa. A bulk density between 3.80 g/cm³and 5.40 g/cm³, preferably between 4.00 g/cm³ and 4.80 g/cm³, may beachieved. In this case, the bulk density is determined in accordancewith EN 993-1.

Due to the lower thermal conductivity, respectively better thermalinsulation properties, compared to dense alumina refractories, Zr basedrefractory lining members with a thick Zr based part such e.g. where theZr base refractory lining member is a shaped refractory according to thepresent invention may be advantageously used in setups where heattransition is an additional critical parameter.

For example, in the manhole area of vessels, operating the non-catalyticprocess, the temperature at the metallic outside shell of the combustionchamber may reach a material-critical value when lined with densealumina refractories at the hot face. In order to avoid a prematureshut-down, a forced outside cooling would be absolutely necessary. Wheninstalling a zirconia based refractory lining member instead of aluminarefractories, the outside temperature may be decreased with increasingthickness of the zirconia layer.

For example in vessels, operating the catalytic steam reforming process,even underneath the bottom lining of the combustion chamber,alumina-volatilization has been found to take place from the catalystwithin the uppermost part of the catalyst bed when the catalyst ismainly based on an alumina-based support material. Thealumina-volatilization may be reduced by installing adequate thickzirconia based refractory lining members in the bottom of the combustionchamber for better heat insulation. As described above, a very lowdecrease in temperature may have a strong impact on the degree ofvolatilization, which may also result in a prolongation of the catalystruntime.

Besides an improved resistance against material volatilization andadvantageous better thermal insulation properties compared to aluminarefractories, shaped zirconia based refractory lining members accordingto the present invention provide another advantageous feature when beinginstalled in the bottom of the combustion chamber of a vessel operatingthe catalytic process. Due to their higher bulk density, they are lessprone to movement and displacement by the fluid dynamic gas flow in thecombustion chamber than dense alumina refractories of the samelayer-thickness.

Thus, the present invention provides a versatile Zr based refractorylining member which may be in form of a Zr coated refractory and/or inform of a shaped Zr based refractory lining member. The variousembodiments provide unprecedented possibilities for solutions for designof linings in e.g. combustion chambers where the different advantageousfeatures of the coated and shaped Zr based refractory lining members maybe applied to achieve a highly optimized and specialized inner liningtaking into account the reducing atmosphere, elevated temperatures andhigh process pressures prevailing in the combustion chamber duringoperation.

The present invention also relates to a refractory lining in acombustion chamber operating in a reducing atmosphere, comprising one ormore of the Zr based refractory lining members described herein.

EXAMPLES AND FIGURES

The object of the invention is described in greater detail in theaccompanying drawings and following examples without thereby limitingthe object of the invention. Examples and figure are not to be construedas limiting to the invention.

Example 1

FIG. 1 is a cross-sectional electro microscopic image showing thestructure of a zirconia based refractory lining member in form of acoating on a Al₂O₃ based refractory material according to the invention(89 times enlarged). The fine-grained crack-free coating isapproximately 250 μm to 300 μm thick and firmly bonded to thecoarse-grained alumina refractory.

A conditioned powder dispersion having a consistency similar tohouse-paints was applied in a layer of a thickness of approximately 500μm by way of spraying onto an untreated surface (approximately 230mm×114 mm) of an alumina refractory brick (Al₂O₃-content approximately99.6 wt. %). The average grain size of the partially stabilized fusedZrO₂-powder used was 11.75 μm (laser diffraction), and the solidscontent of the powder dispersion was 68 wt. %. The coated and driedbrick was thermal treated at a temperature well above 1200° C. Due tothe drying and in particular the thermal treatment, the coating wascompacted to a total thickness of approximately 250 μm, which is in anadvantageous matter accompanied with the formation of a very highstrength, an excellent connection of the coating onto the aluminasubstrate.

Determined by X-ray powder diffraction, the macroscopic crack-freecoating had a total content of tetragonal and cubic ZrO₂ of 46 wt. %,the measured silica content was 0.20 wt. and the alumina-content was3.30 wt. %.

For further tests, coated specimens of approximately 65 mm×45 mm×20 mmwere taken out of the sample, which represents 65 mm×45 mm of the hotface surface. A specimen was heated to a temperature of approximately950° C. and subsequently quenched in cold water. Even after four furthercycles of rapid temperature changes (heating and water quenching), nomacroscopically detectable formation of cracks was found. A secondspecimen was treated five times by thermal cycling within a temperaturerange from room temperature to approximately 1400° C. The heating andcooling rates were approximately 100° C./h, as above without detectabledamages. No detachment of the coating was observed after repeated cyclesof rapid temperature changes i.e. it was found that the coating wasbonded to the substrate.

Examples 2 and 3

In preparing shaped Zr based refractory lining members two differentprepared batch compositions were shaped to bricks having a thickness ofabout 100 mm and a weight of about 10-15 kg, whereby uniaxial pressingprocedure was used (about 80 MPa pressing pressure). After appropriatedrying, the bricks were then fired at 1720° C. The raw-material batchcomposition of example no. 2 was adjusted to reach a total content oftetragonal and cubic ZrO₂ after firing of about 90 wt. whereby fullystabilized fused ZrO₂ was used as raw-material basis. Accordingly, thecomposition of the Example No. 3 was calculated to reach a total contentof tetragonal and cubic ZrO₂ after firing of below 20 wt. % by using ablend of monoclinic and partially stabilized fused ZrO₂. The grain sizeused in Example No. 2 and 3 was 0-2.5 mm, whereby the grading fractionof less than 63 μm had an amount of approx. 25 wt.-%.

After firing, the properties of a brick of Example No. 2 were asfollows: bulk density of 4.60 g/cm³, cold crushing strength of 70 MPa,SiO₂-content of 0.10 wt. Al₂O₃-content of 0.31 wt. and 87 wt. % of totalcontent of tetragonal and cubic ZrO₂; no macroscopically detectableformation of cracks were found. A brick sample was also treated fivetimes by thermal cycling within a temperature range from room toapproximately 1400° C. without macroscopically detectable crackformation. The heating and cooling rates were about 100° C./h.

Bricks of Example no. 3 showed strong cracking already after theproduction-firing. The measured total content of tetragonal and cubicZrO₂ was 17 wt. % (SiO₂-content of 0.40 wt. Al₂O₃-content of 0.20 wt.%).

The improved performance of Zirconia based refractory lining membersaccording to the present invention, both the coated and the brick(shaped refractory) embodiment, were successfully demonstrated in thecombustion chamber of a vessel for industrial production of syngas usingthe catalytic process. During demonstration the material was subjectedto thermal cycling repeatedly. The demonstrated zirconia materialsshowed themselves to be superior to conventional alumina bricks. An upto 85% reduction of the material volatilization was found and thematerial retained its structural integrity and stability post operation.

FIGS. 2a and 2b show a combustion chamber in a gasification reactorwhich may form an integral part of the synthesis gas generation sectionof plants for production of chemicals such as methanol, ammonia andsynthetic fuels. The feed is introduced at the top of the gasificationunit through line (1) and converted to H₂ and CO in the combustionchamber (b) by the burner (a) with air or oxygen introduced through line(2). The synthesis gas product leaves the reformer through an outletchannel line (3). The combustion chamber (b) is enclosed by combustionchamber lining comprising wall tiles (c) and a partitioning channel (d)and/or partitioning layer (d) to downstream sections. In FIG. 2b thepartitioning to downstream section is in form of a permeable refractorymaterial layer of a hold-down material (d) placed on the top of a fixedbed of catalyst pellets (e) separating the combustion chamber from theunderneath situated catalyst bed. The uppermost surface of thepartitioning (d) act as the bottom lining of the combustion chamber. Theburner (a) can be a generic shower head burner, but often more complexburners including high degrees of swirl are used. Such burners generatehigh flow velocities, which can be high enough to move the catalystpellets. Such movement leads to ball milling of the catalyst resultingin degradation of the catalyst pellets and fouling of the bed with thedust produced. Therefore, to prevent this, the top of the bed is coveredwith a layer of large pieces of a refractory hold-down material,typically manufactured from a high alumina material, either as ahydraulic presses or a castable refractory material. These materials aremuch larger than the catalyst pellets and are not affected by the gasmovement.

FIGS. 3a and 3b show to embodiments of Zr based refractory members 4according to the present invention. In FIG. 3a the Zr based refractorymember consists of a single Zr based part 5 only. I.e. the Zr basedrefractory member is shaped refractory in form of a solid brick. In 3 bthe Zr based refractory member comprise a Zr based part 5 in form of acoating on a shaped refractory 7 such as an alumina based refractory. Arefractory lining according to the present invention may comprise solidbricks (shaped refractories) as shown in 3 a and/or coated bricks asshown in FIG. 3 b.

1. A combustion chamber operating in a reducing atmosphere comprising arefractory lining, wherein the refractory lining comprises a shaped andfired zirconia refractory material based on granular stabilized fusedzirconia raw material low in silica, consisting essentially ofcrystalline zirconia, wherein the fired refractory material comprises atotal content of tetragonal and cubic ZrO₂ measured by X-ray powderdiffraction analysis of at least 20% by weight, wherein the tetragonalZrO₂ is in the t-phase, wherein the Al₂O₃ content is 0.05-6% by weight,and wherein the SiO₂ content of bonding phase of the material is below1.5% by weight.
 2. A combustion chamber operating in a reducingatmosphere according to claim 1, wherein the shaped and fired zirconiarefractory material has a thickness of 100 μm-250 mm.
 3. A combustionchamber operating in a reducing atmosphere according to claim 1, whereinthe refractory lining comprises at least part of an inner hot face walllining and/or a partition to downstream.
 4. A combustion chamberoperating in a reducing atmosphere according to claim 1, wherein thecombustion chamber is a combustion chamber for producing syngascomprising H₂ and CO.
 5. A combustion chamber operating in a reducingatmosphere according to claim 1, wherein the raw material is stabilizedby Y₂O₃, MgO, CaO, CeO₂ or mixtures thereof.
 6. A combustion chamberoperating in a reducing atmosphere according to claim 1, wherein thezirconia refractory material is shaped in form of a coating layer on anAl₂O₃-based refractory material.
 7. A combustion chamber operating in areducing atmosphere according to claim 6, wherein the coating layer hasa thickness of 150 μm-500 μm.
 8. A combustion chamber operating in areducing atmosphere according to claim 1, wherein the raw material hasan average grain size of 5 μm to 25 μm.